As one of the negative pressure type booster devices, for example, JP 2008-24293 A discloses a negative pressure type booster device that has a booster shell formed by a front shell and a rear shell, a power piston that divides the interior of the booster shell into a negative pressure chamber and a variable pressure chamber and that is movable in a front-back direction, and a tie rod bolt that hermetically penetrates through the booster shell and a movable partition wall provided in the power piston and that is fixed to the booster shell, the negative pressure chamber being configured to be formed between the front shell and the power piston and connected to a negative pressure source, and the variable pressure chamber being configured to be formed between the rear shell and the power piston and connected to the negative pressure chamber or atmosphere.
In the negative pressure type booster device disclosed in the above-described JP 2008-24293 A, the tie rod bolt hermetically penetrates through a diaphragm as one component of the movable partition wall, and in order to ensure sealing performance of the penetration portion, an annular sealing portion and a tubular guide portion are provided on the diaphragm. In addition, the tubular guide portion permits the required sealing performance to be obtained in the annular sealing portion, by suppressing tilting of the sealing portion with respect to the tie rod bolt such that the annular sealing portion appropriately engages with an outer circumference of the tie rod bolt.
In the negative pressure type booster device disclosed in above-described JP 2008-24293 A, the tubular guide portion is provided on the negative pressure chamber side (front side) with respect to the annular sealing portion. For this reason, during a forward full stroke of the power piston (during movement), there is a concern that the tubular guide portion provided in the diaphragm abuts against an annular member provided in the front shell (a member that hermetically seals between the front shell and the tie rod bolt). In this case, at the time of seal inspection of the annular sealing portion (specifically, inspection that checks the sealing performance by applying a differential pressure to the negative pressure chamber and the variable pressure chamber in the forward full stroke state of the power piston), there is a concern that the sealing performance is also obtained at a contact portion between the guide portion and the annular member, and thus it may not be possible to accurately inspect the sealing performance of the annular sealing portion.
As a consideration for the above-described sealing inspection accuracy, it is also possible to set the tubular guide portion provided in the diaphragm so as not to abut against the annular member provided in the front shell (specifically to increase the width (length in the front-back direction) of the booster shell or to decrease the length in the front-back direction of the guide portion), in the forward full stroke state of the power piston. In this case, however, the booster device increases in size in the front-back direction or the function of the guide portion deteriorates, and thus the sealing performance may be impaired.